A CT scanner includes an x-ray tube mounted on a rotatable gantry that rotates around an examination region about a longitudinal or z-axis. A detector array subtends an angular arc opposite the examination region from the x-ray tube. The detector array detects radiation that traverses the examination region and a subject or object therein and generates a signal indicative thereof. The detector array generally includes a scintillator array optically coupled to a photosensor array, which is electrically coupled to processing electronics. The scintillator array generates light indicative of radiation impinging thereon, the photosensor array generates an electrical signal indicative of the light, and the processing electronics includes an analog-to-digital (A/D) converter that generates digital data indicative of the detected radiation based on the electrical signal. The digital data is processed to generate a signal, which is reconstructed to generate volumetric image data and one or more images therefrom.
A CT scanner has utilized a current to frequency (I/F) converter as the A/D converter. However, this converter is limited in spatial accuracy in low signal, low-dose imaging procedures. By way of example, FIG. 8 shows a diagram illustrating output pulses (“OP”) of the I/F converter as a function of integration period (“IP”). In this diagram, T1 represents the beginning of an integration period. First, second, . . . , L pulses are generated at T2, T3, . . . TL. TM represents the end of the integration period and the beginning of a next integration period. In this example, a next pulse is generated at TN, which occurs in the next integration period. The region 802 represents charge of the first integration period that overlaps the next integration period. The data has been re-aligned to compensate for this, which improves signal to noise, but it also creates skewing of the data in time, which reduces spatial accuracy. Unfortunately, approaches to overcome the spatial skewing have required an increase in circuitry area, cost and power requirements.